I believe there's an easy way to wire a three way switch into your fans, allowing you to run at full-speed/off/half-speed, based on the three switch positions. It may be a cheap solution rather than buying variable speed designed fans. I tried to re-locate the link I had seen this explained and demoed on but I couldn't. Maybe someone with more electrical exp. than I knows about the wiring, resistors and other setup and can help you build such a thing. If I find the link I'll update this post. Best of luck...